/*
 * Copyright (C) 2010 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;

import java.util.ArrayList;
import java.util.LinkedList;

/**
 * Tests the speed of iteration of different iteration methods for collections.
 *
 * @author David Richter
 */
public class IteratorBenchmark
{
    @Param({"0", "1", "16", "256", "4096", "65536"})
    int size;

    // use concrete classes to remove any possible polymorphic overhead?
    Object[] array;
    ArrayList<Object> arrayList;
    LinkedList<Object> linkedList;

    @BeforeExperiment
    void setUp()
    {
        array = new Object[size];
        arrayList = Lists.newArrayListWithCapacity(size);
        linkedList = Lists.newLinkedList();

        for (int i = 0; i < size; i++)
        {
            Object value = new Object();
            array[i] = value;
            arrayList.add(value);
            linkedList.add(value);
        }
    }

    @Benchmark
    int arrayIndexed(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (int index = 0; index < size; index++)
            {
                sum += array[index].hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayIndexedLength(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (int index = 0; index < array.length; index++)
            {
                sum += array[index].hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayFor(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (Object value : array)
            {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListIndexed(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (int index = 0; index < size; index++)
            {
                sum += arrayList.get(index).hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListIndexedLength(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (int index = 0; index < arrayList.size(); index++)
            {
                sum += arrayList.get(index).hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListFor(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (Object value : arrayList)
            {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListToArrayFor(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (Object value : arrayList.toArray())
            {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int linkedListFor(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (Object value : linkedList)
            {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int linkedListToArrayFor(int reps)
    {
        int sum = 0;
        for (int i = 0; i < reps; i++)
        {
            for (Object value : linkedList.toArray())
            {
                sum += value.hashCode();
            }
        }
        return sum;
    }
}
